1. Field of the Invention
This invention concerns a method of operating an air-supplied type coating booth and, more specifically, it relates to a method of operating an air-supplied type coating booth in which conditioned air supplied from an air supply blower to a plenum chamber is enforced to the inside of a tunnel-shaped coating booth where articles to be coated such as car bodies are continuously conveyed and the air in the coating booth is drawn to exhaust together with coating mists, evaporated organic solvents and the likes by an exhaust blower to the beneath of a floor.
2. Description of the Prior Art
In an air-supplied type coating booth for use in coating in which spray coating is conducted, for example, on car bodies continuously conveyed on a conveyor, an elongate tunnel-shaped coating booth is disposed in the coating line between a pre-treatment device for coating and a drying furnace for coated articles. Clean conditioned air supplied from an air supply blower to a plenum chamber is enforced downwardly at a predetermined flow velocity into the coating booth and the air in the booth is drawn together with coating mists, evaporated organic solvent and the likes and discharged to the beneath of a floor by an exhaust blower. This downward air flow can prevent the coating mists, dusts or the likes which would otherwise give undesired effects on the coated films from scattering and drifting upwardly thereby favorably maintaining the coating quality and also keeping the health of operators who make preparation for the coating work or conduct manual spray coating in the coating booth.
By the way, if the flow rate of the conditioned air supplied as described above by the air supply blower to the plenum chamber is different from the flow rate of exhaust air drawn to discharge by the exhaust blower to the beneath of the floor of the coating booth, external air containing dusts or the likes flow through the exit and the inlet opened to both ends of the coating booth to the inside thereof thereby degrading the quality of coated articles, or contaminated air containing the coating mists, organic solvents and the likes in the coating booth flows externally and intrudes into the pre-treatment device for coating or drying furnace for coated articles disposed at the upstreamed and the downstream of the booth thereby worsening the circumstantial conditions.
In view of the above, the present inventors et.al have already proposed a method of operating an air-supplied type coating booth, which comprises detecting the flow velocity of air streams flowing into or out of the exit and the inlet opened to both ends of a tunnel-shaped coating booth, and variablly controlling the flow rate of the exhaust air discharged from the exhaust blower depending on the flow rate of air flowing into and out of the booth calculated based on the detected flow velocity, thereby maintaining the balance between the flow rate of the exhaust air and the flow rate of the supplied air to suppress the air from flowing into or out of the coating booth through the exit and the inlet thereof (U. S. patent application Ser No. 789769 filed on Oct. 21, 1985 and how allowed, entitled as "Method of operating an air feed type spray booth").
However, although the imbalance between the flow rate of air supplied from the air supply blower and the flow rate of exhaust air discharge from the exhaust blower resulted during the steady operation state of the coating booth can be effectively amended by this operation method, it still leaves a problem that it is difficult to rapidly attain a balance between the flow rate for the supplied air and the flow rate for the exhaust air thereby maintaining a stable state where the air streams flow neither into nor out of the coating booth through the exit and the inlet at the start of the booth operation by starting the air supply blower and the exhaust blower.
That is, the air supply blower and the exhaust blower have usually been operated manually upon starting the operation of the air-supplied type coating booth so as to obtain predetermined flow rates for the supplied air and the exhausted air in the conventional method. Since it is very much difficult to attain an ideal balanced state where air streams flow neither into and out of the coating booth through the exit and the inlet when the predetermined stable state is reached after starting the operation of the air supply blower and the exhaust blower. Accordingly, when the booth operation is re-started after the end of recess time or holiday, it takes an extremely long time till the a complete control is obtained in which the flow rate for the supplied air and the flow rate for the exhaust upon thereby worsening the working efficiency.